Selective Power Amplifier

ABSTRACT

A transmitter comprising a power amplifier, a phase modulator, a switched DC-DC converter, all operating in dual mode, and a controller is disclosed. The power amplifier is arranged to selectively operate either in a first mode or in a second mode, wherein the first mode is a linear mode and the second mode is a non-linear mode in order to save power with least increasing cost in hardware. The transmitter is adapted to operate at different allocated bandwidths, for different radio standards while keeping minimum power consumption governed by the controller. A transceiver, a communication device, a method and a computer program are also disclosed.

RELATED APPLICATIONS

This application is a continuation of a U.S. patent application Ser. No.15/184,550, filed 16 Jun. 2016, which is a continuation of U.S. patentapplication Ser. No. 14/366,542, filed 18 Jun. 2014, which is a nationalstage entry under 35 U.S.C. §371 of international patent applicationserial no. PCT/SE2012/051345, filed 5 Dec. 2012, which claims priorityto and the benefit of U.S. provisional patent application Ser. No.61/582,541, filed 3 Jan. 2012, as well as to EP application 11194588.7,filed 20 Dec. 2011. The entire contents of each of the aforementionedapplications is incorporated herein by reference.

TECHNICAL FIELD

The present invention generally relates to a transmitter arranged tooperate in different modes depending on allocated bandwidth oftransmission, and to a corresponding transceiver, communication device,method and computer program.

BACKGROUND

Reduction of energy consumption in radio devices is always desired, andparticularly for radio devices that rely on battery. Most energy isconsumed when transmitting, and a power amplifier, having its task toprovide the radio power to antenna, will of course consume some amountof energy. However, not all energy provided as supply power to the poweramplifier becomes signal power for the radio signal. Thus, the poweramplifier and the transmitter have a degree of power efficiency, i.e.signal power in relation to supply power. It is therefore a desire toprovide a radio, and a way to operate it, which provide good efficiency.

SUMMARY

An object of the invention is to at least alleviate the above statedproblem. The present invention is based on the understanding that, whenusing a radio in communication systems allowing a multitude oftransmission scenarios in sense of allowed or devised transmissionproperties, depending on transmission properties, and especiallyallocated bandwidth, the most efficient, and still feasible with regardto side effects, among polar modulation operation and envelope trackingoperation of a power amplifier and closely related circuitry of thetransmitter can be selected such that quality of operation is improvedin sense of low energy consumption and low impact of non-desired sideeffects. That is, polar modulation is preferred to be used due to itsrelatively low energy consumption as long as side effects, such asspectral leakage, is within reasonable limits, and by this idea, theenvelope tracking is used otherwise to maintain proper transmission. Thepower amplifier can thus be operated in non-linear, and thus energysaving, mode as much as possible, and then be operated in linear, butmore energy consuming, mode when that is necessary. The allocatedbandwidth is the most important factor for deciding when to use whichmode, but this disclosure also provides approaches for furtheradaptation to the circumstances, such as considering modulation type,output power, error vector magnitude and/or spectral leakage requirementfor the transmission to be made by the transmitter, wherein energyconsumption can be held down when any possibility for that is given bythe transmission properties.

According to a first aspect, there is provided a transmitter comprisinga power amplifier; a switch mode voltage converter of directcurrent-to-direct current type arranged to provide power supply to thepower amplifier; and a controller. The power amplifier is arranged toselectively operate in a first mode or in a second mode, wherein thefirst mode is a linear mode and the second mode is a non-linear mode.The controller is arranged to, when operating in a radio accesstechnology, RAT, allowing different allocated bandwidths to be utilised,determine allocated signal bandwidth for a transmission to be made bythe transmitter in the RAT, and the controller comprises a controlmechanism arranged to control the power amplifier to select one of thetransmission modes for the transmission based on the determination.

In the second mode, the power amplifier may be adapted to polarmodulation operation, and the switch mode voltage converter may bearranged to modulate supply voltage to the power amplifier by anamplitude component of the transmission when in the second mode.

The control mechanism may comprise a look-up table comprising bandwidthmapped on operation mode such that operation mode is selectedaccordingly.

The control mechanism may comprise a bandwidth threshold such that thefirst mode is selected if the threshold is exceeded and the second modeis selected otherwise.

The controller may be arranged to select mode such that a requirement onany of output power, error vector magnitude and spectral leakagerequirement for the transmission to be made by the transmitter set by aspecification for the RAT is met.

The first mode may comprise envelope tracking, and wherein the switchmode voltage converter is arranged to provide a supply voltagecorresponding to the output voltage of the power amplifier with aheadroom when in the first mode.

The switch mode voltage converter may further comprise an additionalswitch arrangement connected at the output of the switch mode voltageconverter and an additional comparator connected to compare the outputof the switch mode voltage converter with a determined envelope leveland arranged to control the additional switch arrangement, wherein theadditional switch arrangement and the additional comparator are enabledwhen in the first mode and envelope tracking is used.

The transmitter may further comprise a low-pass filter which isconnected between an output of the switch mode voltage converter and apower supply input of the power amplifier, and wherein the low-passfilter is arranged to have a selectable first and second cut-offfrequencies, wherein the second cut-off frequency is lower than thefirst cut-off frequency, and the low-pass filter is arranged to applythe first cut-off frequency when in the first mode, and the secondcut-off frequency when in the second mode.

The transmitter may further comprise a dual mode modulator arranged toprovide a linear quadrature modulation when in the first mode, andprovide a phase modulation in the second mode. The dual mode modulatormay comprise inputs arranged to receive quadrature baseband signals forin-phase, I, and quadrature, Q, components and radio carrier quadratureclock signals; a quadrature mixer; a transform circuit arranged tooutput the components I and Q unchanged in the first mode, and output,respectively,

$\frac{I}{\sqrt{I^{2} + Q^{2}}}\mspace{14mu} {and}\mspace{14mu} \frac{Q}{\sqrt{I^{2} + Q^{2}}}$

in the second mode, to the quadrature mixer; and a limiter (302),wherein an aggregate output of the quadrature mixer is selectablyconnected to an output of the dual mode modulator either via the limiterwhen in the second mode or directly when in the first mode.

The power amplifier, when selectively operated in the first mode or inthe second mode, may be biased such that in the first mode it isarranged to operate at class A or AB, and in the second mode may bearranged to operate in class D or E.

According to a second aspect, there is provided a transceiver comprisinga transmitter according to the first aspect and a receiver, wherein thetransceiver is arranged to receive information about the signaltransmission bandwidth for a transmission to be made by the transmitterfrom a remote communication node.

According to a third aspect, there is provided a communication devicefor wireless communication, wherein the communication device comprises atransmitter according to the first aspect or a transceiver according tothe second aspect.

The communication device may be arranged to operate in a 3GPP LTEcellular communication system and the transmission is an uplinktransmission, and further arranged to determine the allocated bandwidthfor the uplink transmission based on allocated resource blocks indicatedin a downlink transmission four subframes prior the uplink transmission.

According to a fourth aspect, there is provided a method of atransmitter comprising a power amplifier and a switch mode voltageconverter arranged to provide power supply to the power amplifier. Themethod comprises operating the transmitter in a radio access technology,RAT, allowing different allocated bandwidths to be utilised; determiningallocated signal bandwidth for a transmission to be made by thetransmitter in the RAT; and selecting an operation mode of the poweramplifier among a first mode or a second mode based on the determinedallocated bandwidth, wherein the first mode is a linear mode and thesecond mode is a non-linear mode.

The second mode may include operating the power amplifier for polarmodulation, and the method further comprises modulating supply voltageto the power amplifier by an amplitude component of the transmissionwhen in the second mode.

The method may further comprise receiving information about the signaltransmission bandwidth for a transmission to be made by the transmitterfrom a remote communication node.

The method may further comprise comparing the allocated bandwidth with abandwidth threshold; and selecting the first mode if the threshold isexceeded, or selecting the second mode otherwise.

The method may further comprise determining a modulation to be used forthe transmission to be made by the transmitter; and selecting mode alsobased on the modulation. The method may further comprise determining anyof output power, error vector magnitude and spectral leakage requirementfor the transmission to be made by the transmitter; and selecting modesuch that a requirement on any of the output power, error vectormagnitude and spectral leakage requirement for the transmission set by aspecification for the RAT is met.

The first mode may comprise envelope tracking, and the method furthercomprises providing, when in the first mode, by the switch mode voltageconverter, a supply voltage corresponding to the output voltage of thepower amplifier with a headroom.

A low-pass filter may be connected between an output of the switch modevoltage converter and a power supply input of the power amplifier. Themethod may then further comprise selecting among a first and secondcut-off frequencies of the low-pass filter, wherein the second cut-offfrequency is lower than the first cut-off frequency, and applying thefirst cut-off frequency when in the first mode, and applying the secondcut-off frequency when in the second mode.

The transmitter may further comprise a dual mode modulator. The methodmay then further comprise providing a linear quadrature modulation whenin the first mode, and providing a phase modulation in the second mode,by the dual mode modulator.

The method may further comprise providing quadrature baseband signalsfor in-phase, I, and quadrature, Q, components and radio carrierquadrature clock signals, when in the first mode, to a quadrature mixer,or providing

$\frac{I}{\sqrt{I^{2} + Q^{2}}}\mspace{14mu} {and}\mspace{14mu} \frac{Q}{\sqrt{I^{2} + Q^{2}}}$

when in the second mode, to the quadrature mixer; and limiting theoutput of the quadrature mixer and providing the limited signal asoutput of the dual mode modulator when in the second mode, or providingthe output of the quadrature mixer as output of the dual mode modulatorwhen in the first mode.

The method may further comprise biasing the power amplifier to operatein class A or AB when in the first mode, or biasing the power amplifierto operate in class D or E when in the second mode.

According to a fifth aspect, there is provided a computer programcomprising computer executable code which when executed on a processorcauses a transmitter associated with the processor to perform the methodaccording to the fourth aspect.

Other objectives, features and advantages of the present invention willappear from the following detailed disclosure, from the attacheddependent claims as well as from the drawings. Generally, all terms usedin the claims are to be interpreted according to their ordinary meaningin the technical field, unless explicitly defined otherwise herein. Allreferences to “a/an/the [element, device, component, means, step, etc.]”are to be interpreted openly as referring to at least one instance ofsaid element, device, component, means, step, etc., unless explicitlystated otherwise. The steps of any method disclosed herein do not haveto be performed in the exact order disclosed, unless explicitly stated.

BRIEF DESCRIPTION OF THE DRAWINGS

The above, as well as additional objects, features and advantages of thepresent invention, will be better understood through the followingillustrative and non-limiting detailed description of preferredembodiments of the present invention, with reference to the appendeddrawings.

FIG. 1 illustrates a transmitter circuit according to an embodiment.

FIG. 2 schematically illustrates a transmitter circuit according to anembodiment.

FIG. 3 schematically illustrates a dual-mode modulator according to anembodiment.

FIG. 4 schematically illustrates a pulse width modulation converteraccording to an embodiment.

FIG. 5 illustrates operation of a pulse width modulation converter inwide band mode according to an embodiment.

FIG. 6 illustrates operation of a pulse width modulation converter innarrow band mode according to an embodiment.

FIG. 7 illustrates supply voltage to power amplifier when operating inpolar modulation mode.

FIG. 8 illustrates supply voltage to power amplifier when operating inenvelope tracking mode, and also illustrates a corresponding amplifiedsignal.

FIG. 9 schematically illustrates a switch mode voltage converter set-upaccording to an embodiment.

FIG. 10 schematically illustrates cut-off frequencies for a low-passfilter arranged to filter output from switch mode voltage converter inrespective operation modes.

FIG. 11 schematically illustrates a delay adjustment mechanism arrangedto match delay between amplitude path and phase path according to anembodiment.

FIG. 12 is a flow chart illustrating a method according to anembodiment.

FIG. 13 is a flow chart illustrating a method according to anembodiment.

FIG. 14 is a flow chart illustrating a method according to anembodiment.

FIG. 15 schematically illustrates a non-transitory computer readablestorage medium holding a computer program arranged to be executed by aprocessor to implement methods according to embodiments.

FIG. 16 schematically illustrates a radio circuit comprising atransmitter circuit according to embodiments.

FIG. 17 schematically illustrates a communication device comprising aradio circuit according to embodiments.

FIG. 18 illustrates a communication device according to an embodiment.

FIG. 19 illustrates a communication node according to an embodiment.

FIGS. 20 to 22 illustrate an example where a non-linear mode can beused.

FIGS. 23 to 25 illustrate examples where linear mode needs to be used.

DETAILED DESCRIPTION

For the understanding of this disclosure, the reader should be awarethat polar modulation enables use of a nonlinear power amplifier (PA),which is power efficient, but implies bandwidth expansion issues. Usingpolar modulation is thus not suitable for wide bandwidth applicationslike wide band 3GPP LTE where bandwidths of 20 MHz can be used. A linearPA with a constant supply voltage does not imply such bandwidthexpansion issues, but is significantly less power efficient than anon-linear PA. The linear PA can be made more power efficient by usingenvelope tracking. Envelope tracking requires use of a linear PA, whichis inherently less power efficient than the non-linear PA, but is stillmore efficient than a PA without envelope tracking, i.e., a constantsupply voltage driven PA. High power efficiency implies that more radiopower is provided to the antenna and/or less heat is created by thepower amplifier at a given supply power.

FIG. 1 illustrates a transmitter circuit 100 according to an embodiment.The transmitter circuit 100 comprises a baseband part 106 arranged toperform any baseband processing and provide an in-phase (I) and aquadrature-phase (Q) signal component to be modulated. The transmittercircuit 100 further comprises a power amplifier 102 arranged to output amodulated signal for transmission, e.g. directly to an antennaarrangement or to an antenna arrangement via an output network arrangedto provide impedance matching. The transmitter circuit 100 alsocomprises a switch mode voltage converter 104 arranged to provide asupply voltage to the power amplifier 102. The switch mode voltageconverter 104 is preferably a direct current to direct current, DC/DC,converter which in turn is connected to a power supply of any apparatusin which the transmitter circuit 100 is arranged to work.

To achieve improved efficiency for the transmitter circuit 100, thepower amplifier 102 is arranged to selectively work in either linear ornon-linear modes. The non-linear mode enables improved efficiency forthe power amplifier, which then for example can work in class D or E.The linear mode is less efficient, but provides necessary linearity formany signal situations, e.g. to avoid spectral leakage which extendsbeyond desired levels, and the power amplifier can for example work inclass A or AB. To benefit from this dual mode operation of the poweramplifier, modulation is selectively chosen between quadraturemodulation, which requires linear operation of the power amplifier, andpolar modulation, which enables the power amplifier to work innon-linear mode.

In this embodiment, a polar modulator 108 transform the I and Qcomponents into a phase component which is provided to the poweramplifier. A corresponding amplitude component is provided by anamplitude generator 110 which derives the amplitude component from the Iand Q components and provides the amplitude component to the switchedvoltage generator 104 which in turn controls the voltage supply to thepower amplifier such that the amplitude component together with thephase component can be output by the power amplifier as a polarmodulated signal.

Similarly, a quadrature modulator 112 modulates the I and Q componentsby mixing with an in-phase oscillator signal and a quadrature-phaseoscillator signal, respectively, and an aggregate of the modulated I andQ components are provided to the power amplifier. The amplitudegenerator 110 is now used for envelope tracking and is providing, basedon the I and Q components, an envelope signal to the switch mode voltageconverter 104 such that it provides a suitable supply voltage to thepower amplifier, wherein the power amplifier is enabled to work linearlyand amplify the aggregate of the modulated I and Q components. Theenvelope signal tracks the envelope of the amplitude signals of the Iand Q components, and provides a suitable headroom for linear operationby the power amplifier.

The transmitter circuit 100 is controlled to select the most efficientof the modes of operation based on the properties of the signal to betransmitted. This control can be provided from the baseband part 106, orfrom a dedicated controller (not shown). The property of the signal tobe transmitted having most impact on which mode that is suitable to beused is allocated bandwidth. The decision provided by the control can befairly simple, such as when the bandwidth is 5 MHz or below in an 3GPPLTE case, polar modulation and non-linear power amplifier operation ischosen, and above that, quadrature modulation and linear operation ofthe power amplifier is chosen. A more complex control can be providedwhere modulation properties of the I and Q components from the basebandpart are considered, i.e. how signal space is used. This can be usedtogether with the information on allocated bandwidth to for example forsome configurations of the I and Q components use polar modulation andnon-linear power amplifier operation also for slightly higherbandwidths, while for some other configurations of the I and Qcomponents use quadrature modulation and linear power amplifieroperation also for slightly lower bandwidths. Similar considerations forselecting mode of operation can be made based on one or more of outputpower, error vector magnitude and spectral leakage requirement for thetransmission to be made by the transmitter. Thus, although the allocatedbandwidth plays the major role in the selection, further optimisationcan be made for mid-sized bandwidths based on used signal space, outputpower, error vector magnitude and/or spectral leakage requirement.

The selection of quadrature modulation/linear operation or polarmodulation/non-linear operation can be determined according to what isdemonstrated above such that spectral leakage does not extend beyond thespecification of the system in which the transmitter is used, e.g.beyond what is specified in 3GPP TS25.101, 3GPP TS 36.101, or similarfor the actual system.

The knowledge about the signal to be transmitted, and thus the decisionabout which mode of operation to select, can many times be acquired abit in advance, which facilitates the implementation. For example, in3GPP LTE, an uplink grant message is received four subframes in advance,which equals four ms, wherein the transmitter is aware of allocatedbandwidth etc. and the adaptation of the mode can be made.

The operation of the power amplifier 102 in linear or non-linear modecan of course be achieved by selectively using either of a linear poweramplifier or a non-linear power amplifier, i.e. having separate poweramplifiers. However, to avoid having redundant circuitry, the control ofmode of operation of the power amplifier can include adapting biasing ofone power amplifier to selectively either operate in linear or innon-linear mode. An output network can also be adapted to the mode ofoperation of the power amplifier to take care of any unwanted harmonics.

FIG. 2 schematically illustrates a transmitter circuit 200 according toan embodiment. A baseband processor, BBP, 212 generates I and Qcomponents similar to what is demonstrated with reference to FIG. 1. TheI and Q components are fed into two paths, the amplitude path (upwardsin FIG. 2) and the phase path (rightwards in FIG. 2). The amplitude pathincludes an envelope/amplitude generator, EAG, 214, a pre-distortion,PDIS, part 216, a pulse width modulation converter, PWMC, 218, a switchmode voltage converter 204, a low pass filter, LPF, 208, and a dual modepower amplifier, DMPA, 202. The phase path includes a delay adjust unit,DA, 220, a dual mode modulator, DMM, 210, and the DMPA 202 where the twopaths are merged together. The DMM 210 is provided with carrierquadrature clocks, CQC, such that modulation is enabled. The CQC cancomprise four signals being mutually phase shifted by 90 degrees fordifferential mixers, or two signals being mutually phase shifted by 90degrees for single ended mixers.

A controller 206 is arranged to control the elements of the transmittercircuit 100 to operate according to a first operation mode, i.e.quadrature modulation and linear amplifier setting, and to a secondoperation mode, i.e. polar modulation and non-linear amplifier setting.The first operation mode is typically making the DMPA 202 operating in alinear mode, while the second mode sets the DMPA 202 in a non-linearoperation mode. The output from the switch mode voltage converter isoptionally low-pass filtered by LPF 208 prior to providing the voltagesupply to the DMPA 202. Furthermore, the baseband I and Q components,generated by BBP 212, are converted to envelope or amplitude signal,depending on mode of operation, by EAG 214, and the envelope signal oramplitude signal can be pre-distorted via the PDIS 216 to reducenon-linearity in generating output signal at output of the DMPA 202.This non-linearity can include any contributions from the PWMC 218, theswitch mode voltage converter 204 and the DMPA 202.

Any delay match between phase modulation path and amplitude path can bealigned by the DA 220 under control of the controller 206. The LPF 208can have two modes, one for wide band applications, and one for narrowband applications, selected either by electrical or mechanical means.The function of the LPF 208 is to reduce ripples in the output of theswitch mode voltage converter, improve adjacent channel leakage ratiofor band interferences to meet spectral masks specified by radiostandards, and also suppress transmitter spectral leakage into receiverband when the transmitter circuit 200 is used in a radio terminal, whichimplies relax of requirements for attenuation in receiver band insurface acoustic wave filters or duplexers.

After the DMPA 202, the amplified signal can pass an output network, ON,222 which includes impedance matching that minimize the reflections andfeed the majority of the signal energy to the antenna, and sometimesdifferential to single-ended conversion if balanced power amplifiertopology is adopted. ON 222 can also be capable to reduce the unwantedfrequency components created by non-linearity of the power amplifier.The ON 222 can also be controlled by the controller 206, and be adaptedbased on the operating mode of the power amplifier 202.

The first mode, i.e. linear mode, operation is targeted to applicationsusing wide band, i.e. having a wide allocated bandwidth and/or having amodulation scheme using signal space for large symbols, for example auser scenario in 3GPP LTE using 20 MHz bandwidth. So in linear mode, therequirement for operating frequency or bandwidth is much high for allunits, and the power efficiency drops. However, as the occupation intime normally is short and the probability for this is relatively lowthan operation in narrow band applications, one can bear this energycost.

The second mode, i.e. non-linear mode, is designed to fit most narrowband applications, in multiple standards, for example, GSM, EDGE, etc.,and even the narrow band user scenario in 3GPP LTE up to about 5 MHzallocated bandwidth.

Further functions, operations and options for the elements of thetransmitter circuit 200 will be demonstrated with reference to FIGS. 3to 11.

FIG. 3 schematically illustrates a dual-mode modulator, DMM, 300according to an embodiment. In the phase modulation path in FIG. 2, theDA 220 is employed to match the delay between the amplitude path and thephase path. Depending on the delay in the phase path and amplitude pathfor a practical implementation, the DA 220 can be moved to any positionin either phase path or amplitude path, and be implemented in eitherdigital or analog way. For the purpose of illustration of the DMM 300 inFIG. 3, it is assumed that the DA is provided in the phase path andprovides delayed components Id and Qd to the DMM 300. The dual modemodulator maps the input signals Id and Qd into U and V by a matrix A ina mapping part 304, then the U and V signals are modulated by quadraturecarrier clocks, and a radio frequency signal is created. The matrix Acan be implemented in a look-up table, or RAM or ROM cells. In the firstmode which is used for envelope tracking applications, the mapping part304 just is a bypass having

U=Id

V=Qd

In the second mode, the mapping part performs the following non-linearmapping:

$U = \frac{Id}{\sqrt{{Id}^{2} + {Qd}^{2}}}$$V = \frac{Qd}{\sqrt{{Id}^{2} + {Qd}^{2}}}$

Thus, the U and V signal is amplitude normalized quadrature signals.After quadrature modulation, the output can be expressed as

$V_{m} = \{ {{\begin{matrix}{A_{m}{\sin ( {{\omega \; t} + \phi_{m}} )}} & {{in}\mspace{14mu} {first}\mspace{14mu} {mode}} \\{\sin ( {{\omega \; t} + \phi_{m}} )} & {{in}\mspace{14mu} {second}\mspace{14mu} {mode}}\end{matrix}{where}A_{m}} = {{\sqrt{{Id}^{2} + {Qd}^{2}}\phi_{m}} = {\arctan \lbrack \frac{Qd}{Id} \rbrack}}} $

The above equations imply that in the first mode, the modulator performsa normal linear quadrature modulation, while in the second mode themodulator merges a normal linear quadrature modulation and limiterfunction together.

The limiter function can also be implemented in analog ways, and anexemplary circuit is shown in FIG. 3, where an analog limiter 302 and amultiplexer 306 are used.

FIG. 4 schematically illustrates a pulse width modulation converter 400according to an embodiment. Envelope/amplitude generator EAG 214 of FIG.2 creates a digital envelope or polar modulation amplitude signalaccording to the quadrature digital input I and Q components. To createpolar modulation, a one-to-one mapping is employed

Amp(n)=√{square root over (i ²(n)+q ²(n))}

While for envelope signals, the generation may not be a unique, forexample, the envelope signal can be created by

${{Env}(n)} = {{G_{0}( \sqrt{{i^{2}(n)} + {q^{2}(n)}} )} + {\sum\limits_{m = 0}^{N - 1}\; {{h( {n - m} )}\sqrt{{i^{2}(m)} + {q^{2}(m)}}}}}$

Where h( ) is coefficients of a digital filter, and G₀( ) creates avoltage gap between the max amplitude and supply voltage to guaranteethat the linear power amplifier always operates at linear region.Another example may be

Env(n)=G ₀(√{square root over (i ²(n)+q ²(n))})+max└√{square root over(i ²(n)+q ²(n))}┘

Both envelope signal or amplitude signals can be over-sampled andsmoothed in digital manners.

The output Po of the power amplifier is unfortunately a non-linearfunction of the envelope or amplitude signal, say Po=f(env) orPo=g(amp). In PDIS, signal envelope signal or amplitude signal isnon-linearly mapped into Penv or Pamp by the pre-distortion function Pand Q

-   Penv=p(Env)-   OR-   Pamp=Q(Amp)-   So that-   Po=f(P(Env))=k·Env-   Or-   Po=g(Q(Amp)=k·Amp

Where P or Q is a reverse function of f(·) or G(·) that reduces theamplitude distortion in the amplitude path.

Through PWMC 400, the digital signal P_(env) is converted into pulsewidth modulated pulse sequence PWM, where the pulse width is a functionof the input voltage and the pulse frequency is C. There are manydifferent ways for creating PWM. For example, the pulse width modulatedsequence can be created by cutting a saw-tooth input, provided by asaw-tooth generator 404 with repeat frequency of C_(s), as shown in FIG.4, and the PWMC can have two modes, illustrated in FIGS. 5 and 6 for awide band signal and a narrow band signal, respectively, controlled byCTRL which changes the divider ratio of a frequency divider 402.

The switching frequency of the PWM pulse sequence determines theconversion efficiency of the switch mode voltage converter, as regulatortransistor in the switch mode voltage converter is operating at thisfrequency, and charges and discharges capacitance in the load and LPF,leading to a dynamic power consumption. The dynamic power reduces theconversion efficiency in switch mode voltage converter. According to theparticular user scenario, the controller sets the divider ratiocorresponding to the bandwidth which in turn optimizes the switch modevoltage converter conversion efficiency.

The DC/DC-converter switch mode voltage converter can also operate intwo modes. One is used in narrow bandwidth applications where polarmodulation is implemented, illustrated in FIG. 7, and another is for thelinear mode, i.e. wide band mode, where envelope tracking is performed,shown in FIG. 8.

For the narrow bandwidth applications, the switch mode voltage converterhas the similar structure like a normal DC/DC converter 904, and theslew rate of the output of the converter 904 is enough to follow thechange of Penv as illustrated in FIG. 7. In wide bandwidth applications,an additional fast switch 902 and a fast comparator 906, as illustratedin FIG. 9, can automatically be turned on when bandwidth expansionhappens. The output of the comparator 906 is provided to a logiccircuitry 908 which in turn controls switches of the switch arrangement902.

The LPF 208 of FIG. 2 can optionally be designed to have differentcut-off frequencies, as illustrated in FIG. 10, and the LPF can compriseLC passive devices, MEMS or other semi-conductor switches with lowinsertion loss.

The DMPA has dual operating modes, i.e. the linear mode for working withenvelope tracking and the non-linear mode for polar modulation,corresponding to the bandwidth requirement etc. for differentapplications. The operating mode can be changed by setting the operationpoint of the power amplifier. For example, a power amplifier can operateat class A, or AB for linear operation. To improve the power efficiency,the power amplifier can also be set to operate in non-linear mode, sayclass D or E, without substantively changing the topology of theamplifier, assuming that the output network can remove any unwantedharmonic components. Of course, it is also possible to have both linearpower amplifier and non-linear power amplifier in parallel and each ofthem has an enable control, and only one of them is enabled duringoperation.

FIG. 11 illustrates a DA 1100 according to an embodiment. The I and Qcomponents are fed to a register array 1102 under control of a clocksignal, and are output from output registers 1104 under control of anadjusted clock signal wherein the adjusted clock signal is provided byan adjustable phase shifter 1106 which preferably is controlled by thecontroller 206 of FIG. 2. Depending on the delay in the phase path andamplitude path for a practical implementation, the delay adjust unit canbe moved to any position, either the phase path or amplitude path, andbe implemented in either digital or analog manner.

FIG. 12 is a flow chart illustrating a method according to anembodiment. A transmitter is operated 1200 in a radio access technology,RAT, which for example can be GSM, EDGE, WCDMA or LTE. The allocatedbandwidth for a transmission to be made is determined 1202. Thedetermination can be made, for some RATs such as GSM, fairly simplebecause the RAT only supports bandwidths below a threshold wherenon-linear mode can be used. For other RATs, such as LTE, the allocatedbandwidth can imply any of non-linear, which is preferred due to highefficiency, or linear operation. Thus, the mode of operation for poweramplifier etc. according to what has been demonstrated above isdetermined 1204 such that the transmitter can adapt accordingly andperform the transmission. The procedure repeats itself all the time, andnext transmission may be in another or the same RAT, with anotherallocated bandwidth, and the suitable mode of operation is selected forthat transmission.

FIG. 13 is a flow chart illustrating a method according to anembodiment. A transmitter is operated 1300 in a RAT which for examplecan be GSM, EDGE, WCDMA or LTE. The allocated bandwidth for atransmission to be made is determined 1302. The determination can bemade, for some RATs such as GSM, fairly simple because the RAT onlysupports bandwidths below a threshold where non-linear mode can be used.For other RATs, such as LTE, the allocated bandwidth can imply any ofnon-linear, which is preferred due to high efficiency, or linearoperation. In the case of LTE, the allocated bandwidth will be knownfour subframes in advance from an uplink grant message. The allocatedbandwidth is compared 1304 with a threshold.

If the allocated bandwidth exceeds the threshold, which for example canbe 5 MHz, envelope tracking is applied 1305 and linear mode is selected1307 for the power amplifier. Optionally, a higher cut-off frequency(compared to the one which will be applied for polar modulation) can beselected 1309 for a low-pass filter arranged at output of switch modevoltage converter.

If the allocated bandwidth does not exceed the threshold, polarmodulation is applied 1306 and non-linear mode of operation is selected1308 for the power amplifier. Optionally, a lower cut-off frequency(compared to the one which will be applied for envelope tracking) can beselected 1310 for a low-pass filter arranged at output of switch modevoltage converter.

Thus, the mode of operation for power amplifier etc. according to whathas been demonstrated above is adapted such that the transmitter canperform the transmission as efficiently as possible. The procedurerepeats itself all the time, and next transmission may be in another orthe same RAT, with another allocated bandwidth, and the suitable mode ofoperation is selected for that transmission.

FIG. 14 is a flow chat illustrating a method according to an embodiment.A transmitter is operated 1400 in a RAT which for example can be GSM,EDGE, WCDMA or LTE. Transmission properties, such as modulation, outputpower, error vector magnitude and/or spectral leakage requirement, andthe allocated bandwidth for a transmission to be made is determined1402. The transmission properties are mapped 1404 to a suitable mode ofoperation. The mapping can include accessing a look-up table.

When the transmission properties are mapped to a first operation mode,the power amplifier is adjusted 1405 to linear mode of operation, the Iand Q components provided from baseband are transformed 1407 into anenvelope signal, and the switch mode voltage converter is controlled1409 according to the envelope signal. Further, pre-compensation of theI and Q components can be made 1411, and/or selection of a highercut-off frequency of a LPF as demonstrated above can be made 1413. Thetransmission is made 1415 according to the adaptations and with envelopetracked quadrature modulation as demonstrated above, and the procedurereturns to take care of next transmission.

When the transmission properties are mapped to a second operation mode,the power amplifier is adjusted 1406 to non-linear mode of operation,the I and Q components are transformed 1408 to an amplitude signal, theswitch mode voltage converter is controlled 1410 according to theamplitude signal, and the I and Q components are transformed 1412 to aphase signal, e.g. by being limited either digitally or by an analoglimiter. Further, a lower cut-off frequency of the LPF can be made 1414.The transmission is made 1416 according to the adaptations and withpolar modulation as demonstrated above, and the procedure returns totake care of next transmission.

The methods have been demonstrated with reference to FIGS. 12 to 14 as afew different examples. It should however be understood that someactions in one example can be substituted by corresponding other actionfrom another example, e.g. the step on comparison with a bandwidththreshold can be substituted with mapping of transmission properties, orvice versa. Further, although the steps have been presented as asequential order, this normally does not reflect the operation inreality. The elucidated adaptations are normally performed in parallel,or at least being performed as soon as necessary input data for theadaptation is available. As a few examples, the elements of theamplitude path are adapted simultaneously with the adaptations of theelements of the phase path, and the control of the switch mode voltageconverter is performed during the whole transmission, the determinationof transmission properties for the next transmission is normally startedbefore the previous transmission is ready, etc.

The methods according to the present invention is suitable forimplementation with aid of processing means, such as computers and/orprocessors, especially for example for the case where the suitableoperation mode is to be determined on complex information and/or thesignals provided to modulation in different operation modes are to bedetermined accordingly. Therefore, there is provided computer programs,comprising instructions arranged to cause the processing means,processor, or computer to perform the steps of any of the methodsaccording to any of the embodiments described with reference to any ofFIGS. 12-14. The computer programs preferably comprise program codewhich is stored on a computer readable medium 1500, as illustrated inFIG. 15, which can be loaded and executed by a processing means,processor, or computer 1502 to cause it to perform the methods,respectively, according to embodiments of the present invention,preferably as any of the embodiments described with reference to any ofFIGS. 12-14. The computer 1502 and computer program product 1500 can bearranged to execute the program code sequentially where actions of theany of the methods are performed stepwise. The processing means,processor, or computer 1502 is preferably what normally is referred toas an embedded system. Thus, the depicted computer readable medium 1500and computer 1502 in FIG. 15 should be construed to be for illustrativepurposes only to provide understanding of the principle, and not to beconstrued as any direct illustration of the elements.

FIG. 16 schematically illustrates a radio circuit 1600 according to anembodiment. The radio circuit 1600 comprises a transmitter circuit 1602according to any of the embodiments demonstrated. The transmittercircuit provides its output signal to one or more antennas 1608,possibly via a feeding line and/or output network. The radio circuit1600 can also comprise other radio circuitry 1604, which for example cancomprise a receiver, signal processing device, interface circuit, etc.It is also possible that the radio circuit 1600 can comprise more thanone transmitter circuit 1602, e.g. one being arranged to operate towardsa cellular network and another arranged to operate towards a wirelessaccess point. The radio circuit 1600 can also comprise a controller1606, which for example can provide acquired data about comingtransmission to the transmitter circuit 1602.

FIG. 17 schematically illustrates a communication device 1700 accordingto an embodiment. The communication device comprises a radio circuit1702 according to any of the embodiments demonstrated above. Thecommunication device 1700 also comprises further circuitry and elements1704 such as input and output devices, interfaces, power supply, etc.The radio circuit 1702 is connected to the further circuitry 1704 forprovision or reception of signals that are received or to betransmitted. Further, the further circuitry and elements 1704 canprovide control information to a controller of the radio circuitry 1702.

FIG. 18 schematically illustrates an example of a mobile communicationdevice 1800 according to an embodiment. The mobile communication devicecan be arranged for communication in a cellular communication system andcomprise the elements demonstrated above.

FIG. 19 schematically illustrates an example of a communication node1900 according to an embodiment for operating a cell in a cellularcommunication system. The communication node 1900 can be arranged tooperate a cell in a cellular communication system and comprise theelements demonstrated above.

FIGS. 20 to 22 illustrate an example of a user scenario where polarmodulation can be used. In FIG. 20, the LTE spectrum 2000 for the wholeband in question is shown. The spectrum can be shared by a multitude ofusers. In FIG. 20, a user bandwidth 2002, i.e. allocated bandwidth, isalso shown.

FIG. 21 shows a spectrum of the amplitude of the user occupied resourceblocks. FIG. 22 shows phase modulated radio frequency clock signals. Forsuch a user scenario in LTE uplink with whole spectrum 2000 when a useris scheduled to occupy a few gathered resource blocks with a frequencyoffset 2004 from a centre frequency of the spectrum 2000 and anallocated bandwidth 2002, an amplitude of a baseband signal will have arelatively narrow bandwidth compared to the bandwidth of the LTEspectrum 2000. Thus the transmitter is able to operate in the secondoperating mode and apply polar modulation. The phase modulation pathwill generate phase modulated radio frequency clock signals around thecarrier frequency plus the offset frequency 2004, as illustrated in FIG.22.

FIGS. 23 to 25 illustrate an example of a user scenario where envelopetracking need to be used. In FIG. 23, the LTE spectrum 2300 for thewhole band in question is shown. The spectrum can be shared by amultitude of users. In FIG. 23, a user bandwidth 2302, i.e. allocatedbandwidth, embracing allocated resource blocks distributed in differentfrequency locations is also shown. For such a user scenario in LTEuplink with whole spectrum 2300 when a user is scheduled to occupyresource blocks which are distributed over the spectrum 2300 and thushas an allocated bandwidth 2302 that is almost as wide as the bandwidthof the LTE spectrum 2300. In a first option, the transmitter can operatein the first operating mode preferably with envelope tracking using thecarrier frequency of the centre frequency of the LTE spectrum withbandwidth 2402 shown in FIG. 24. In a second option, the modulator cangenerate quadrature modulated radio frequency clock signals with afrequency around the centre frequency of the LTE spectrum plus an offsetfrequency, as illustrated in FIG. 25, with bandwidth 2502 which is equalto 2302.

The invention has mainly been described above with reference to a fewembodiments. However, as is readily appreciated by a person skilled inthe art, other embodiments than the ones disclosed above are equallypossible within the scope of the invention, as defined by the appendedpatent claims.

Notably, modifications and other embodiments of the disclosedinvention(s) will come to mind to one skilled in the art having thebenefit of the teachings presented in the foregoing descriptions and theassociated drawings. Therefore, it is to be understood that theinvention(s) is/are not to be limited to the specific embodimentsdisclosed and that modifications and other embodiments are intended tobe included within the scope of this disclosure. Although specific termsmay be employed herein, they are used in a generic and descriptive senseonly and not for purposes of limitation.

What is claimed is:
 1. A communication device configured to operate in a3GPP LTE cellular communication system, comprising: a power amplifier;and a switch mode voltage converter of direct current-to-direct currenttype arranged to provide a supply voltage to the power amplifier;wherein the power amplifier is configured to operate in a linear modeduring uplink transmissions with a 20 MHz bandwidth, and in a nonlinearmode during uplink transmissions with a 5 MHz bandwidth.
 2. Thecommunication device of claim 1, wherein the linear mode is an envelopetracking mode.
 3. The communication device of claim 1, wherein thenonlinear mode is a polar modulation mode.
 4. The communication deviceof claim 3, wherein the switch mode voltage converter is configured tomodulate the supply voltage of the power amplifier with an amplitudecomponent of an uplink transmission, when operating in the polarmodulation mode.
 5. The communication device of claim 1, comprising acontroller configured to control the operating mode of the poweramplifier.
 6. A method performed in a communication device configured tooperate in a 3GPP LTE cellular communication system, where thecommunication device includes a power amplifier and a switch modevoltage converter of direct current-to-direct current type arranged toprovide power supply to the power amplifier, the method comprising:operating the power amplifier in a linear mode during uplinktransmissions with a 20 MHz bandwidth, and in a nonlinear mode duringuplink transmissions with a 5 MHz bandwidth.
 7. The method of claim 6,wherein the linear mode is an envelope tracking mode.
 8. The method ofclaim 6, wherein the nonlinear mode is a polar modulation mode.
 9. Themethod of claim 8, comprising modulating, by the switch mode voltageconverter, the supply voltage of the power amplifier with an amplitudecomponent of an uplink transmission, when operating the power amplifierin the polar modulation mode.